Conventionally, in a surround system such as a 5.1-channel system, three speakers of a left speaker, a right speaker, and a center speaker are located in front of a listener, and it is desirable that the center speaker is located between the left speaker and the right speaker. However, since a display apparatus such as a television set is located between a left speaker and a right speaker, it is difficult that a center speaker is located between a left speaker and a right speaker.
Therefore, a surround system is proposed, in which a center speaker is omitted, and a center channel positioning based on a center channel sound signal is virtually formed by a left speaker and a right speaker.
In such a surround system mentioned above, a case will be mentioned, in which a center speaker is located in front of a listener position, and a left speaker is located with an angle of 30° in the left direction from the listener position, and a right speaker is located with an angle of 30° in the right direction from the listener position. A frequency characteristic in the case where a center channel sound signal is reproduced by left and right speakers is compared with a frequency characteristic in the case where the center channel sound signal is actually reproduced by a center speaker. In the case where a center channel sound signal is reproduced by left and right speakers, there is a problem that a gain is lowered by approximately 10 dB at a frequency band of approximately 1 to 4 kHz.
An apparatus for solving the above problem is shown, for example, in Patent Document No. 1.    Patent Document No. 1: Japanese Patent Laid-open No. 2004-266604
In a reproducing apparatus disclosed in Patent Document No. 1 mentioned above, after a center channel sound signal is processed by an equalizer in such a way that its frequency characteristic is corrected, the resultant signal is reproduced by left and right speakers. A characteristic of the equalizer is one which causes a frequency characteristic of a head transfer function in the case where a center channel sound signal is reproduced by left and right speakers to be equal to a frequency characteristic of a head transfer function in the case where the center channel sound signal is actually reproduced by a center speaker.
Concretely, at a frequency band of approximately 1 to 4 kHz, a level of frequency characteristic in the case where a center channel sound signal is reproduced by left and right speakers becomes lower than a level of frequency characteristic in the case where the center channel sound signal is actually reproduced by a center speaker, by approximately 10 dB. Therefore, an equalizer has a characteristic which causes a gain to be raised by approximately 10 dB at a frequency band of approximately 1 to 4 kHz.